U.S. Pat. Nos. 3,083,698 and 3,158,930 disclose brake boosters having a housing manufactured through a well known method wherein an end surface on a first shell is crimped by cutting or shearing tabs that engage a surface on a second shell to define a unitary structure. It is a common practice to spray paint the exterior surface of the shells to protect against oxidation of the shells that are exposed to the environment when installed in a vehicle. The crimped joints function in an adequate manner to seal the interior of the unitary structure for use as a housing for a brake booster. Unfortunately, the painting process while effective often did not provided a uniform protection over the entire exterior surface of a shell and as a result some oxidation could occur after a period of time. In an effort to better protect the shells, a process known as e-coating was developed which uniformly coats the shell and this process is now an accepted standard for protection with respect to oxidation. However, in the crimping process through which the first shell is joined to the second shell certain portions of the first shell are either sheared or stretched such that the sheared portion of the first shell has bare metal exposed to the environment and over a period of time this bare metal oxidizes and creates an undesirable appearance for the brake booster. While it would be possible to re-coat or touch up the bare or exposed metal after crimping, the time, effort and labor involved would add considerable cost to the manufacturing process which a customer would be hesitant to absorb as no tangible functional benefit of the brake booster would occur from such added effort.
U.S. Pat. No. 6,390,567 discloses structure and a method of manufacturing a brake booster wherein essentially all surfaces are protected from exposure to the environment. In this brake booster a first shell a flange having a plurality of slits and slots thereon is deforming mid point of the slots to engage a peripheral surface on a second shell and create a sealed housing. This sealed connection in a stable and non-corrosive condition however under certain conditions, corrosion may occur on the peripheral surface on the second shell as certain portions are exposed to the environment.